Research over the past decade supports the hypothesis that proteostasis (the ability to maintain a healthy proteome) plays a major role in aging. This is based on observations such as: 1) mechanisms that maintain proteostasis decline with age in several animal models and in senescent human fibroblasts, 2) increasing proteostasis leads to an increase in lifespan and healthspan in C. elegans. It is also widely believed that mechanistically, the effect of proteostasis on aging is due to improvements in handling proteotoxicity (the accumulation of misfolded proteins and aberrant protein aggregates), thus protecting the organism against some age-related diseases, most notably neurodegenerative ones. However, almost all of the data on the relationship between longevity and proteotoxicity comes from studies done in short-lived animals, primarily C. elegans and mice. Because of the difference in time scales, it is possible that the mechanisms involved in increasing lifespan in long-lived species such as humans might differ from mechanisms used by invertebrates or even mice. Therefore, it is not clear whether these observations will translate to species such as humans. In this application we will use a comparative biology approach to determine whether enhanced proteostasis and reduced proteotoxicity correlate with the longevity of mammals. We will use 6 species (3 long- and 3 short-lived) that cover a broad spectrum within the mammalian phylogeny to ensure generality of our conclusions. Our preliminary data using these 3 pairs show that long-lived species have enhanced proteostasis compared to the short-lived species from the same clade. Based on our data, we hypothesize that cells from long-lived species will show increased resistant to proteotoxicity. We will test ths hypothesis by using poly-Q constructs transfected into fibroblasts from the panel of long- and short-lived species. First we will determine whether long-lived species, which have improved proteostasis, indeed show improved protection against proteotoxicity, and in Aim 2 we will investigate the molecular pathways involved in proteotoxicity resistance. For this we will measure protein aggregation in the presence of inhibitors for different proteostasis pathways.